Pulmonary Trunk
The pulmonary trunk (truncus pulmonalis) is a large vessel approximately 5–6 cm long and up to 3 cm wide. It originates from the conus arteriosus of the right ventricle. Its orifice features semilunar valves (valvulae semilunares trunci pulmonalis) that prevent the backflow of blood into the heart.
Leaving the right ventricle, the vessel courses anteriorly and to the left, lying anterior and to the left of the ascending aorta. Reaching the level of the 4th thoracic vertebra, the trunk passes beneath the aortic arch and divides into two branches: the right and left pulmonary arteries. This site is termed the bifurcation of the pulmonary trunk (bifurcatio trunci pulmonalis).
Topographical relations of the pulmonary trunk:
- Anteriorly: the ascending aorta.
- Left: the left atrium and its auricle (auricula).
- Right: the ascending aorta and superior vena cava.
Pulmonary Arteries and Their Branching
Following bifurcation, blood is distributed into two arteries, each exhibiting specific anatomical pathways and branching patterns within the lung parenchyma.
Right Pulmonary Artery (a. pulmonalis dextra) Runs almost horizontally, crossing the posterior wall of the ascending aorta and passing posterior to the superior vena cava. Upon reaching the hilum of the right lung, it divides into three lobar branches:
- Superior lobar branch (r. lobi superioris) — supplies the apical, anterior, and posterior segments via respective branches (r. apicalis, r. anterior, r. posterior).
- Middle lobar branch (r. lobi medii) — originates from the inferior branch of the artery and divides into lateral and medial branches (r. lateralis, r. medialis).
- Inferior lobar branch (r. lobi inferioris) — gives off an apical branch (r. apicalis) and four basal branches (rr. basales: medialis, anterior, lateralis, posterior).
Left Pulmonary Artery (a. pulmonalis sinistra) This artery is shorter but wider than the right. It courses to the left, superiorly, and posteriorly, passing behind the ascending aorta, beneath the aortic arch and the left main bronchus. In the left lung, it divides into only two lobar branches:
- Superior lobar branches (rr. lobi superioris) — supply the apicoposterior and anterior segments, and give rise to the superior and inferior lingular branches (rr. lingulares).
- Inferior lobar branches (rr. lobi inferioris) — anatomically similar to the right side, giving off an apical branch and three basal branches (anterior, lateral, and posterior).
Pulmonary Vein System
Oxygenated blood leaves the lungs via the pulmonary venous system (vv. pulmonales). Normally, humans have exactly four such veins: two right and two left. They drain directly into the left atrium, completing the pulmonary circuit.
Superior and inferior veins are formed on each side:
- Right superior pulmonary vein (v. pulmonalis superior dextra) collects blood from structures of the superior and middle lobes of the right lung (apical, anterior, posterior, medial, and lateral veins).
- Right inferior pulmonary vein (v. pulmonalis inferior dextra) drains the inferior lobe via the superior apical and basal venous branches.
- Left superior pulmonary vein (v. pulmonalis superior sinistra) drains the superior lobe and lingular segments of the left lung.
- Left inferior pulmonary vein (v. pulmonalis inferior sinistra), similar to the right inferior vein, drains blood from the basal and apical structures of the inferior lobe.
Topography of the Root of the Lung
Understanding the surgical anatomy of the pulmonary circuit requires knowing the spatial arrangement of structures within the pulmonary roots. Each root comprises the main bronchus (bronchus principalis), one pulmonary artery (a. pulmonalis), and two pulmonary veins (vv. pulmonales).
The syntopy of these elements differs on the right and left sides:
- In the right lung, the pulmonary artery lies strictly anterior to the main bronchus.
- In the left lung, the artery passes superior to the main bronchus.